1. Field of the Invention
The present invention relates to a method of manufacturing pneumatic tyres for vehicle wheels.
The invention also is concerned with an apparatus for manufacturing pneumatic tyres for vehicle wheels.
2. Description of the Related Art
A pneumatic tyre for vehicle wheels generally comprises a carcass structure including at least one carcass ply internally coated with an airtight layer usually referred to as “liner”, and having respectively opposite end flaps turned up loop-wise around annular anchoring structures, each usually consisting of a substantially circumferential annular insert to which at least one filling insert is applied, at a radially external position.
Associated with the carcass structure is a belt structure comprising one or more belt layers, disposed in radial superposed relationship with respect to each other and to the carcass ply and having textile or metallic reinforcing cords with a crossed orientation and/or substantially parallel to the circumferential extension direction of the tyre. Applied to the belt structure at a radially external position is a tread band.
Respective sidewalls of elastomer material are also applied to the side surfaces of the carcass structure, each extending from a so-called “shoulder region” localised close to one of the side edges of the tread, band until close to the respective annular anchoring structure to the beads.
In most of the known production processes use of at least one building drum is provided on which the individual semifinished components of the carcass structure are assembled in a predetermined sequence.
Usually, the belt structure and tread band constitute a so-called “belt package” that is made separately on a respective auxiliary drum to be subsequently assembled to the carcass structure on the building drum in processes of the “unistage” type, or on a so-called “shaping drum” in processes of the “two-stage” type.
In manufacturing tyres for specific or particular uses, integration of additional annular components into the carcass or belt structure may be required.
For example, insertion of the so-called “under-belt elongated elements” of elastomer material may be required, each of said elongated elements extending circumferentially between the carcass structure and one of the side edges of the belt structure. In building self-supporting or run flat tyres, i.e. such made as to enable running under acceptable safety conditions even when the tyre is partly or wholly deflated, additional annular reinforcing inserts are required to be integrated into the carcass structure; said inserts are usually called “sidewall inserts” and their task is substantially to bear the load resting on the wheel when, following a puncture for example, the inflating pressure of the tyre is reduced or is completely absent.
Document U.S. Pat. No. 6,488,797 depicts a run flat tyre provided with sidewall inserts of elastomer material of such a length that it substantially extends from the shoulder region of the tyre to the corresponding bead region. In tyre manufacture, these sidewall inserts are circumferentially disposed to a suitable mutual axial distance on the building drum, before or after application of the liner, and before application of the carcass ply or plies.
The sidewall inserts are usually made starting from at least one continuous strip of elastomer material obtained by extrusion, from which segments of appropriate length are cut out. Each segment is circumferentially applied around the building drum, and the extremities of same are end-to-end joined.
In the process described in DE-10 2004 008 306, the sidewall inserts are made separately of the tyre being manufactured on the building drum by joining the extremities of a semifinished product in the form of a strip on a flat surface, so as to improve the end-to-end joint quality. The sidewall inserts are subsequently engaged on the building drum to be associated with the other tyre components. Alternatively, the sidewall inserts can be directly made in the form of a loop without joining points, by injection moulding for example, and subsequently transferred onto the building drum.
Document US-2003/102,088 discloses a manufacturing method according to which several different tyre components, among which the sidewall inserts for a run flat tyre, are formed through spiral winding of a strip of raw elastomer material on an outer circumferential surface of the building drum.
In document WO-2005/105419, in the name of the same Applicant, a method of building run flat tyres is proposed in which the sidewall inserts are made on a service drum to be subsequently transferred onto the building drum on which assembling of the components of the carcass structure is carried out. Each sidewall insert is formed through winding of a continuous elongated element of elastomer material into coils disposed consecutively in side by side relationship on the service drum. Thus circumferential discontinuities and other faults are eliminated, which faults are due to the presence of end-to-end joints for example in the inserts obtained from segments of an extruded strip.